Phillips Flat Countersunk Head Self Tapping Screws
Also known as cross recessed flat countersunk head self tapping screws.
18-8 stainless steel screws have good chemical resistance and may be mildly magnetic. They're beveled under the head for use in countersunk holes.
316 stainless steel screws are more corrosion resistant than 18-8 stainless steel screws, these have excellent resistance to chemicals and salt water and may be mildly magnetic.
410 stainless steel screws are stronger and more wear resistant than 18-8 and 316 stainless steel, these screws are magnetic and mildly chemical resistant. They're not for use with aluminum sheet metal.
Zinc-plated steel screws resist corrosion in wet environments.
Nickel-plated steel screws have a decorative finish and are more corrosion resistant than zinc-plated screws.
Black-oxide steel screws are mildly corrosion resistant in dry environments.